FreeBSD makes only limited amount of DMA memory available for drivers. The sblive driver implements several parallel audio devices. The vmix (virtual mixing) driver adds few more of them and the system will run out of memory.

As a workaround you can edit /usr/lib/oss/etc/installed_drivers and to remove the line containing "vmix". After a reboot OSS should work again.

Actually the right place is in kernel/OS/FreeBSD/os_freebsd.c. Change the "int size = 64 * 1024;" line in the beginning of __oss_alloc_dmabuf(). Dropping the "64" to 32 or even 16 should fix the problem. However anything below 64k will break application(s) that assume 64k buffers (I recall it was RealPlayer).